This invention relates to a metal terminal to be crimped to an electric wire.
Generally, a metal terminal to be crimped to an electric wire includes a base plate portion for the placing of the electric wire thereon, and a pair of crimping piece portions extending upwardly respectively from opposite side edges of the base plate portion. A crimper of a crimping machine for pressing the pair of crimping piece portions includes a groove having an inner surface formed by a pair of arch-shaped curved surfaces disposed symmetrically (with respect to a central plane of the crimper) in adjoining relation to each other. The pair of crimping piece portions slide respectively on the curved surfaces of the groove in the crimper, and are bent or curved along the respective curved surfaces, and are press-fastened to the electric wire.
There has been proposed one conventional metal terminal in which distal end portions of a pair of crimping piece portions are so shaped as to increase the force (strength) of holding of an electric wire by the crimping piece portions press-fastened to the electric wire (see JP-A-5-190214).
As shown in FIG. 7, in JP-A-5-190214, a tapered surface 53 is formed on an outer side (outer surface) of the distal end portion of each crimping piece portion 51 of the metal terminal 50 in such a manner that an angle θ of the tapered surface 53 relative to a distal end surface 52 is not smaller than 70 degrees. With this configuration, the distal end portion of each crimping piece portion 51 can be easily plastically deformed, and therefore the pair of crimping piece portions 51 can be positively press-fastened to the electric wire so as to increase the wire holding force.
In JP-A-5-190214, when a thickness D of the crimping piece portion 51 at the distal end surface 52 is too small, the wire holding force is reduced. On the other hand, when the thickness D is too large, the crimping piece portion can not be easily plastically deformed. For these reasons, the thickness D is set to about ½ of a plate thickness T of the crimping piece portion 51. However, even when the thickness D at the distal end surface 52 is fixed to ½ of the plate thickness T to thereby increase the angle θ of the tapered surface 53 relative to the distal end surface 52, the amount of change (decrease) in the cross-sectional area of the distal end portion is small, and therefore the amount of plastic deformation of the distal end portion can not be sufficiently increased.
The distal end portions of the pair of crimping piece portions 51 are curved toward each other by the respective curved surfaces of the crimper, and strike against each other at their distal ends. Upon striking of the distal ends against each other, the pair of crimping piece portions 51 exert loads respectively on their mating crimping piece portions 51 so as to further plastically deform the distal end portions toward the electric wire. When the distal end portions of the crimping piece portions 51 curved by the respective curved surfaces of the crimper are not sufficiently plastically deformed, a contact angle obtained upon striking of the distal ends against each other is increased. Furthermore, the contact angle increases with the increase of the angle θ of the tapered surface 53 relative to the distal end surface 52.
When the contact angle between the pair of crimping piece portions 51 is large, the loads mutually acting respectively on the distal end portions do not serve to plastically deform the distal end portions toward the electric wire, so that the crimped shape is unstable. That the crimped shape is unstable means that the stable wire holding force can not be secured.